1. Technical Field of the Invention
The present invention relates to a drive controller for controlling driving of a power conversion circuit, and to a drive control system, and in particular, to a drive control circuit which is provided with a power ON/OFF electrical switching element and is suitable for a power conversion circuit that uses a technique of converting voltage with the operation of the switching element, and to a drive control system equipped with the power conversion circuit and the drive controller.
2. Related Art
Known electrode conversion circuits include one which is provided with a switching element that can be electrically turned ON/OFF. Such a conversion circuit is configured such that the switching element is repeatedly turned ON/OFF to increase/decrease the absolute value of the current passing through the coil. With this repeated operation, voltage of the power storage means is converted to the voltage having a desired value as requested by the power supply means.
Generally, in a drive controller used for such a power conversion circuit, a parasitic capacitor is electrically connected parallel to the input/output terminals of the switching element. Therefore, when the switching element is switched from an OFF state to an ON state, short circuit may occur, via the switching element, between the electrodes of the parasitic capacitor. For this reason, if the parasitic capacitor has been charged when the state is switched to an ON state, this switch-ON operation will permit the charges of the parasitic capacitor to pass through the switching element, by which power loss may be caused.
Under the circumstances, some measures have been taken, as can be seen in Japanese Patent Application Laid-Open Publication No. 2005-512491, for example. This reference suggests that, after the current that passes through the coil of a power conversion circuit has been zeroed, a predetermined standby time is given preceding the switch-ON operation. Thus, when current is passed through the closed loop circuit including the coil and the parasitic capacitor, the charges of the parasitic capacitor can be extracted.
The amount of charges extracted from the parasitic capacitor when current is passed through the closed loop circuit, depends on the voltage (input voltage) of the power supply means and the voltage (output voltage) of the power storage means of the power conversion circuit. Therefore, depending on the relationship between the input voltage and the output voltage, not all the charges of the parasitic capacitor can be extracted. In this case, flow of charges of the parasitic capacitor through the switching element in switching the state of the switching element to an ON state, can cause power loss.